blue and white LEDs in the 70s?

Retromaster · Post by **Retromaster** » Mon Jan 22, 2007 1:31 pm

why weren't blue and white leds around in the 70's?
they had other colors. and this means you couldn't led mod a screen back then. SHEER AGONY!!!Oh wait...they didn't have LCD screens back then....

loup · Post by **loup** » Mon Jan 22, 2007 2:12 pm

actually, they did have white LEDs, but they weren't commercially available, but I think the real answer here is that LED technology just hadn't progressed that far yet.

Retromaster · Post by **Retromaster** » Mon Jan 22, 2007 2:30 pm

everything back then was ancient. the stella processor in the atari seems like a grain of salt compared to nowadays tech.

Post by **Skyone** » Mon Jan 22, 2007 6:20 pm

They didn't have yellow, purple, ultraviolet, orange and many other colors in the 1970s, because LEDs became commercial in the 1970s (orignally invented ~1960.) Blue is the high of the spectrum (and takes up the most energy,) which is why it came available in the 1990s.

By the way, LCDs were invented in the early 1970s.

Retromaster · Post by **Retromaster** » Mon Jan 22, 2007 6:25 pm

By the way, LCDs were invented in the early 1970s.

You mean the LCDs in those calculators you see everywhere now?
I doubt you could find color LCDs....did they have them?

And when they first figured out certain diodes could emmit light, it must have been a semi-colorful world without all the good colors.
What's so different about the chemistry of blue LEDs and basic colored LEDs?

timmeh87 · Post by **timmeh87** » Mon Jan 22, 2007 7:08 pm

in the p-n junction of any diode, there is a release of energy associated with the recombination of the electrons and holes (the electron falls into the hole and releases energy). in normal diodes, this energy doesnt radiate, for whatever quantum-mechanical reason i dont understand.

LEDs are diodes made of 'direct band gap' materials, which do radiate a photon when the electrons recombine. The process of photon emission is similar to the one that produces emission in (for example) neon signs. Band gaps are a complicated topic, but the important part is that the width of the band gap determines the wavelength of the photon.

different color LEDs are therefore made with different combinations of semiconductor material, tailored to have a very specific band gap - determined by what color you want it to be.

for whatever reason not explained on wikipedia, it was easier back in the 70's to make gallium arsenide based leds, which have the smallest band gap and the shortest wavelength: infrared - red. for quite some time, this sufficed. tv remotes and indicator lights were enough of a novelty back then i guess.

advances in science have obviously made led technology a lot better since then, and we now have a rainbow of led colors to choose from, made from a wide array of semiconductors like aluminum, arsenic, indium, and even diamond.

blue leds were not invented till the 1990s, as stated. Ultraviolet ones came even later. since blue is a part of white light, white leds could not have existed before the 1990's.

however, most white leds today are either blue or ultraviolet leds with a phosphor coating, the former use a yellow phosphor to balance out the blue, the ultraviolet ones operate much like fluorescent lights.